Lightest Supersymmetric Particle Mass Research Articles

(g−2)μ and SUSY

The persistent [Formula: see text] discrepancy between the experimental result from Brookhaven National Laboratory (BNL) for the anomalous magnetic moment of the muon, [Formula: see text], and its Standard Model (SM) prediction, was confirmed recently by the “MUON G-2” result from Fermilab. The combination of the two measurements yields a deviation of [Formula: see text] from the SM value. Here, we review an analysis of the parameter space of the electroweak (EW) sector of the Minimal Supersymmetric Standard Model (MSSM), which can provide a suitable explanation of the anomaly while being in full agreement with other latest experimental data like the direct searches for EW particles at the LHC and dark matter (DM) relic density and direct detection constraints. Taking the lightest supersymmetric particle (LSP) (the lightest neutralino in our case) to be the DM candidate, we discuss the case of a mixed bino/wino LSP, which can account for the full DM relic density of the universe and that of wino and higgsino DM, where we take the relic density only as an upper bound. We observe that an upper limit of [Formula: see text] can be obtained for the LSP and next-to (N)LSP masses establishing clear search targets for the future HL-LHC EW searches, but in particular for future high-energy [Formula: see text] colliders such as the ILC or CLIC.

Improved {(g-2)_mu } measurements and wino/higgsino dark matter

The electroweak (EW) sector of the Minimal Supersymmetric Standard Model (MSSM) can account for a variety of experimental data. In particular it can explain the persistent 3-4,sigma discrepancy between the experimental result for the anomalous magnetic moment of the muon, (g-2)_mu , and its Standard Model (SM) prediction. The lightest supersymmetric particle (LSP), which we take as the lightest neutralino, {tilde{chi }}_{1}^0, can furthermore account for the observed Dark Matter (DM) content of the universe via coannihilation with the next-to-LSP (NLSP), while being in agreement with negative results from Direct Detection (DD) experiments. Concerning the unsuccessful searches for EW particles at the LHC, owing to relatively small production cross-sections a comparably light EW sector of the MSSM is in full agreement with the experimental data. The DM relic density can fully be explained by a mixed bino/wino LSP. Here we take the relic density as an upper bound, which opens up the possibility of wino and higgsino DM. We first analyze which mass ranges of neutralinos, charginos and scalar leptons are in agreement with all experimental data, including relevant LHC searches. We find roughly an upper limit of sim 600 ,, mathrm {GeV} for the LSP and NLSP masses. In a second step we assume that the new result of the Run 1 of the “MUON G-2” collaboration at Fermilab yields a precision comparable to the existing experimental result with the same central value. We analyze the potential impact of the combination of the Run 1 data with the existing (g-2)_mu data on the allowed MSSM parameter space. We find that in this case the upper limits on the LSP and NLSP masses are substantially reduced by roughly 100 ,, mathrm {GeV}. We interpret these upper bounds in view of future HL-LHC EW searches as well as future high-energy e^+e^- colliders, such as the ILC or CLIC.

Cold Dark Matter in SUSY Theories. The Role of Nuclear Form Factors and the Folding with the LSP Velocity.

The momentum transfer dependence of the total cross section for elastic scattering of cold dark matter candidates, i.e. lightest supersymmetric particle (LSP), with nuclei is examined. We find that even though the energy transfer is small (<100 keV) the momentum transfer can be quite big for large mass of the LSP and heavy nuclei. The total cross section can in such instances be reduced by a factor of about five. The spin induced cross section for odd-A nuclei is less reduced since the high multipoles tend to enhance the cross section as the momentum transfer increases (for LSP mass < 200 GeV). We present calculations of the event rates for a number of nuclear targets in a relatively wide phenomenologically allowed SUSY parameter space. These event rates are folded with a Maxwellian velocity distribution of the LSP consistent with its density hi the halos. We thus find that the event rates due to the Earth's revolution around the sun can change by 25%. This factor seems to be quite independent of the other parameters of the theory. Event rates up to 80 Kg^{-1}y^{-1} can be obtained in the parameter space considered.

Search for bottom-squark pair production with the ATLAS detector in final states containing Higgs bosons, b-jets and missing transverse momentum

The result of a search for the pair production of the lightest supersymmetric partner of the bottom quark left({tilde{b}}_1right) using 139 fb−1 of proton-proton data collected at sqrt{s} = 13 TeV by the ATLAS detector is reported. In the supersymmetric scenarios considered both of the bottom-squarks decay into a b-quark and the second-lightest neutralino, {tilde{b}}_1to b+{tilde{chi}}_2^0 . Each {tilde{chi}}_2^0 is assumed to subsequently decay with 100% branching ratio into a Higgs boson (h) like the one in the Standard Model and the lightest neutralino: {tilde{chi}}_2^0to h+{tilde{chi}}_1^0 . The {tilde{chi}}_1^0 is assumed to be the lightest supersymmetric particle (LSP) and is stable. Two signal mass configurations are targeted: the first has a constant LSP mass of 60 GeV; and the second has a constant mass difference between the {tilde{chi}}_2^0 and {tilde{chi}}_1^0 of 130 GeV. The final states considered contain no charged leptons, three or more b-jets, and large missing transverse momentum. No significant excess of events over the Standard Model background expectation is observed in any of the signal regions considered. Limits at the 95% confidence level are placed in the supersymmetric models considered, and bottom-squarks with mass up to 1.5 TeV are excluded.

Discovery reach for wino and higgsino dark matter with a disappearing track signature at a 100 TeV pp collider

Within the theory of supersymmetry, the lightest neutralino is a dark matter candidate and is often assumed to be the lightest supersymmetric particle (LSP) as well. If the neutral wino or higgsino is dark matter, the upper limit of the LSP mass is determined by the observed relic density of dark matter. If the LSP is a nearly-pure neutral state of the wino or higgsino, the lightest chargino state is expected to have a significant lifetime due to a tiny mass difference between the LSP and the chargino. This article presents discovery potential of the 100 TeV future circular hadron collider (FCC) for the wino and higgsino dark matter using a disappearing-track signature. The search strategy to extend the discovery reach to the thermal limits of wino/higgsino dark matter is discussed with detailed studies on the background rate and the reference design of the FCC-hadron detector under possible running scenarios of the FCC-hadron machine. A proposal of modifying the detector layout and several ideas to improve the sensitivity further are also discussed.

Search for squarks and gluinos in final states with hadronically decaying τ -leptons, jets, and missing transverse momentum using pp collisions at s=13 TeV with the ATLAS detector

A search for supersymmetry in events with large missing transverse momentum, jets, and at least one hadronically decaying $\tau$-lepton is presented. Two exclusive final states with either exactly one or at least two $\tau$-leptons are considered. The analysis is based on proton-proton collisions at $\sqrt{s}$ = 13 TeV corresponding to an integrated luminosity of 36.1 fb$^{-1}$ delivered by the Large Hadron Collider and recorded by the ATLAS detector in 2015 and 2016. No significant excess is observed over the Standard Model expectation. At 95% confidence level, model-independent upper limits on the cross section are set and exclusion limits are provided for two signal scenarios: a simplified model of gluino pair production with $\tau$-rich cascade decays, and a model with gauge-mediated supersymmetry breaking (GMSB). In the simplified model, gluino masses up to 2000 GeV are excluded for low values of the mass of the lightest supersymmetric particle (LSP), while LSP masses up to 1000 GeV are excluded for gluino masses around 1400 GeV. In the GMSB model, values of the supersymmetry-breaking scale are excluded below 110 TeV for all values of $\tan\beta$ in the range $2 \leq \tan\beta \leq 60$, and below 120 TeV for $\tan\beta>30$.

Search for supersymmetry with Higgs boson to diphoton decays using the razor variables at [formula omitted

An inclusive search for anomalous Higgs boson production in the diphoton decay channel and in association with at least one jet is presented, using LHC proton–proton collision data collected by the CMS experiment at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 35.9fb−1. The razor variables MR and R2, as well as the momentum and mass resolution of the diphoton system, are used to categorize events into different search regions. The search result is interpreted in the context of strong and electroweak production of supersymmetric particles. We exclude bottom squark pair-production with masses below 450 GeV for bottom squarks decaying to a bottom quark, a Higgs boson, and the lightest supersymmetric particle (LSP) for LSP masses below 250 GeV. For wino-like chargino–neutralino production, we exclude charginos with mass below 170 GeV for LSP masses below 25 GeV. In the GMSB scenario, we exclude charginos with mass below 205 GeV for neutralinos decaying to a Higgs boson and a goldstino LSP with 100% branching fraction.

Scenarios for gluino coannihilation

We study supersymmetric scenarios in which the gluino is the next-to-lightest supersymmetric particle (NLSP), with a mass sufficiently close to that of the lightest supersymmetric particle (LSP) that gluino coannihilation becomes important. One of these scenarios is the MSSM with soft supersymmetry-breaking squark and slepton masses that are universal at an input GUT renormalization scale, but with non-universal gaugino masses. The other scenario is an extension of the MSSM to include vector-like supermultiplets. In both scenarios, we identify the regions of parameter space where gluino coannihilation is important, and discuss their relations to other regions of parameter space where other mechanisms bring the dark matter density into the range allowed by cosmology. In the case of the non-universal MSSM scenario, we find that the allowed range of parameter space is constrained by the requirement of electroweak symmetry breaking, the avoidance of a charged LSP and the measured mass of the Higgs boson, in particular, as well as the appearance of other dark matter (co)annihilation processes. Nevertheless, LSP masses $m_\chi \lesssim 8$~TeV with the correct dark matter density are quite possible. In the case of pure gravity mediation with additional vector-like supermultiplets, changes to the anomaly-mediated gluino mass and the threshold effects associated with these states can make the gluino almost degenerate with the LSP, and we find a similar upper bound.

Status and prospects of the nMSSM after LHC Run-1

The new minimal supersymmetric standard model (nMSSM), a variant of the general next to minimal supersymmetric standard model (NMSSM) without $Z_3$ symmetry, features a naturally light singlino with a mass below 75 GeV. In light of the new constraints from LHC Run-1 on the Higgs couplings, sparticles searches and flavour observables, we define the parameter space of the model which is compatible with both collider and dark matter (DM) properties. Among the regions compatible with these constraints, implemented through NMSSMTools, SModelS and MadAnalysis 5, only one with a singlino lightest supersymmetric particle (LSP) with a mass around 5 GeV can explain all the DM abundance of the universe, while heavier mixed singlinos can only form one of the DM components. Typical collider signatures for each region of the parameter space are investigated. In particular, the decay of the 125 GeV Higgs into light scalars and/or pseudoscalars and the decay of the heavy Higgs into charginos and neutralinos, provide distinctive signatures of the model. Moreover, the sfermion decays usually proceed through heavier neutralinos rather than directly into the LSP, as the couplings to the singlino are suppressed. We also show that direct detection searches are complementary to collider ones, and that a future ton-scale detector could completely probe the region of parameter space with a LSP mass around 65 GeV.

Search for supersymmetry in events with soft leptons, low jet multiplicity, and missing transverse energy in proton–proton collisions at s=8 TeV

Results are presented from a search for supersymmetric particles in scenarios with a compressed mass spectrum. The data sample corresponds to 19.7 inverse femtobarns of proton-proton collisions recorded by the CMS experiment at sqrt(s) = 8 TeV. The search targets top squark pair production in scenarios with mass differences Delta m = m(top squark) - m(neutralino) below the W-boson mass and with top-squark decays in the four-body mode (top squark to b l nu neutralino), where the neutralino is assumed to be the lightest supersymmetric particle (LSP). The signature includes a high transverse momentum (pt) jet associated with initial-state radiation, one or two low-pt leptons, and significant missing transverse energy. The event yields observed in data are consistent with the expected background contributions from standard model processes. Limits are set on the cross section for top squark pair production as a function of the top squark and LSP masses. Assuming a 100% branching fraction for the four-body decay mode, top-squark masses below 316 GeV are excluded for Delta m = 25 GeV at 95% CL. The dilepton data are also interpreted under the assumption of chargino-neutralino production, with subsequent decays to sleptons or sneutrinos. Assuming a difference between the common lightest chargino/next lightest neutralino mass and the LSP mass of 20 GeV and a tau-enriched decay scenario, masses in the range m(chargino) < 307 GeV are excluded at 95% CL.

Supersymmetry with a heavy lightest supersymmetric particle

To escape the current LHC supersymmetry (SUSY) search constraints while preserving the naturalness condition, we propose the heavy lightest supersymmetric particle (LSP) SUSY. According to the different dependencies on the LSP mass, we systematically classify the discriminating variables into three categories. We find that the strong dependence of all current SUSY searches on variables in the first category render weak sensitivity for the heavy LSP SUSY. In particular, all the current LHC SUSY search constraints can be evaded if the LSP mass is around 600 GeV or higher. In the minimal supersymmetric standard model (MSSM), we find that the heavy LSP SUSY does not induce more fine-tuning than the Higgs boson mass. Moreover, the muon anomalous magnetic moment can be satisfied within the 3-σ level. We systematically study the viable parameter space for the heavy LSP SUSY and present four benchmark points that realize our proposal concretely. An improved collider search for those benchmark points, which mainly relies on the variable in the second category, is discussed in detail.

Search for top squark pair production in final states with one isolated lepton, jets, and missing transverse momentum in s $$ \sqrt{s} $$ = 8 TeV pp collisions with the ATLAS detector

The results of a search for top squark (stop) pair production in final states with one isolated lepton, jets, and missing transverse momentum are reported. The analysis is performed with proton--proton collision data at $\sqrt{s} = 8$ TeV collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of $20$ fb$^{-1}$. The lightest supersymmetric particle (LSP) is taken to be the lightest neutralino which only interacts weakly and is assumed to be stable. The stop decay modes considered are those to a top quark and the LSP as well as to a bottom quark and the lightest chargino, where the chargino decays to the LSP by emitting a $W$ boson. A wide range of scenarios with different mass splittings between the stop, the lightest neutralino and the lightest chargino are considered, including cases where the $W$ bosons or the top quarks are off-shell. Decay modes involving the heavier charginos and neutralinos are addressed using a set of phenomenological models of supersymmetry. No significant excess over the Standard Model prediction is observed. A stop with a mass between $210$ and $640$ GeV decaying directly to a top quark and a massless LSP is excluded at $95$ % confidence level, and in models where the mass of the lightest chargino is twice that of the LSP, stops are excluded at $95$ % confidence level up to a mass of $500$ GeV for an LSP mass in the range of $100$ to $150$ GeV. Stringent exclusion limits are also derived for all other stop decay modes considered, and model-independent upper limits are set on the visible cross-section for processes beyond the Standard Model.

Phenomenology in supersymmetric neutrinophilic Higgs model with sneutrino dark matter

We study a supersymmetric neutrinophilic Higgs model with large neutrino Yukawa couplings where neutrinos are Dirac particles and the lightest right-handed (RH) sneutrino is the lightest supersymmetric particle (LSP) as a dark matter candidate. Neutrinophilic Higgs bosons need to be rather heavy by the precise determination of the muon decay width and dark radiation constraints for large Yukawa couplings. From the Large Hadron Collider constraints, neutrinophilic Higgsino mass need to be heavier than several hundred GeV or close to the RH sneutrino LSP mass. The latter case is interesting because the muon anomalous magnetic dipole moment can be explained with a relatively large lightest neutrino mass, if RH sneutrino mixings are appropriately fine tuned in order to avoid stringent lepton flavor violation constraints. Dark matter is explained by asymmetric RH sneutrino dark matter in the favoured region by the muon anomalous magnetic dipole moment. In other regions, RH sneutrino could be an usual WIMP dark matter.

Search for Stop Pair Production at the LHC using the CMS Detector

A search for pair production of top squark events in proton-proton collisions at a center-of-mass energy of √s = 8 TeV is performed in a sample with a single isolated electron or muon, jets, large missing transverse energy and large transverse mass. The data sample used corresponds to an integrated luminosity of 19.5 fb−1 collected by the CMS experiment. No significant excess in data is observed above the expectation from standard model processes. In the context of supersymmetric models with pair production of top squarks decaying to either a top quark and the lightest supersymmetric particle (LSP) or a bottom quark and a chargino that subsequently decays to a W boson and the LSP, the results probe top squarks with masses up to about 650 GeV for LSP masses up to about 250 GeV.

Search for Direct Top Squark Pair Production in Final States with One Isolated Lepton, Jets, and Missing Transverse Momentum ins=7 TeVppCollisions Using4.7 fb−1of ATLAS Data

A search is presented for direct top squark pair production in final states with one isolated electron or muon, jets, and missing transverse momentum in proton-proton collisions at sqrt[s] = 7 TeV. The measurement is based on 4.7 fb(-1) of data collected with the ATLAS detector at the LHC. Each top squark is assumed to decay to a top quark and the lightest supersymmetric particle (LSP). The data are found to be consistent with standard model expectations. Top squark masses between 230 GeV and 440 GeV are excluded with 95% confidence for massless LSPs, and top squark masses around 400 GeV are excluded for LSP masses up to 125 GeV.

Non-thermal Higgsino dark matter, heavy gravitino and 125 GeV Higgs boson in modulus/anomaly-mediated supersymmetric models

If the lightest supersymmetric particle (LSP) is Higgsino-like, the thermal relic density is lower than the observed dark matter content for a LSP mass in the sub-TeV region. We outline constraints arising from the Fermi Gamma-ray Telescope data and LSP production from gravitino decay that must be satisfied by a successful nonthermal Higgsino scenario. We show that in a generic class of models where anomaly- and modulus-mediated contributions to supersymmetry breaking are of comparable size, Higgsino arises as the only viable sub-TeV dark matter candidate if gravitinos are heavy enough to decay before the onset of big bang nucleosynthesis. The correct relic density can be obtained via modulus decay in these models. As an explicit example, we consider a modulus sector in effective field theory ($D=4$, $N=1$ supergravitiy arising from type IIB Kachru-Kallosh-Linde-Trivedi compactification). Within this class of mirage mediation models, heaviness of the gravitino forces a sub-TeV Higgsino LSP and gives a Higgs mass around 125 GeV. In this example, the constraints from direct detection experiments are also satisfied.

Supersoft supersymmetry is super-safe

We show that supersymmetric models with a large Dirac gluino mass can evade much of the jets plus missing energy searches at the LHC. Dirac gaugino masses arise from ``supersoft'' operators that lead to finite one-loop suppressed contributions to the scalar masses. A little hierarchy between the Dirac gluino mass 5--10 times heavier than the squark masses is automatic and technically natural, in stark contrast to supersymmetric models with Majorana gaugino masses. At the LHC, colored sparticle production is suppressed not only by the absence of gluino pair (or associated) production, but also because several of the largest squark pair production channels are suppressed or absent. We recast the null results from the present jets plus missing energy searches at the LHC for supersymmetry onto a supersoft supersymmetric simplified model. Assuming a massless lightest supersymmetric particle, we find the strongest bounds are as follows: 748 GeV from a $2j+{\mathrm{E\ensuremath{\llap{\not\;}}}}_{T}$ search at ATLAS ($4.7\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$) and 684 GeV from a combined jets plus missing energy search using ${\ensuremath{\alpha}}_{T}$ at CMS ($1.1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$). In the absence of a future observation, we estimate the bounds on the squark masses to improve only modestly with increased luminosity. We also briefly consider the further weakening in the bounds as the lightest supersymmetric particle mass is increased.

Where is SUSY?

The direct searches for Superymmetry at colliders can be complemented by direct searches for dark matter (DM) in underground experiments, if one assumes the Lightest Supersymmetric Particle (LSP) provides the dark matter of the universe. It will be shown that within the Constrained minimal Supersymmetric Model (CMSSM) the direct searches for DM are complementary to direct LHC searches for SUSY and Higgs particles using analytical formulae. A combined excluded region from LHC, WMAP and XENON100 will be provided, showing that within the CMSSM gluinos below 1 TeV and LSP masses below 160 GeV are excluded (m_{1/2} > 400 GeV) independent of the squark masses.

Spread Supersymmetry

In the multiverse the scale of supersymmetry breaking, $$ \widetilde{m} = {F_X}/{M_{ * }} $$ ∗, may scan and environmental constraints on the dark matter density may exclude a large range of m from the reheating temperature after inflation down to values that yield a lightest supersymmetric particle (LSP) mass of order a TeV. After selection effects, for example from the cosmological constant, the distribution for $$ \widetilde{m} $$ in the region that gives a TeV LSP may prefer larger values. A single environmental constraint from dark matter can then lead to multi-component dark matter, including both axions and the LSP, giving a TeV-scale LSP somewhat lighter than the corresponding value for single-component LSP dark matter. If supersymmetry breaking is mediated to the Standard Model sector at order X † X and higher, only squarks, sleptons and one Higgs doublet acquire masses of order $$ \widetilde{m} $$ . The gravitino mass is lighter by a factor of M ∗ /M Pl and the gaugino masses are suppressed by a further loop factor. This Spread Supersymmetry spectrum has two versions, one with Higgsino masses arising from supergravity effects of order the gravitino mass giving a wino LSP, and another with the Higgsino masses generated radiatively from gaugino masses giving a Higgsino LSP. The environmental restriction on dark matter fixes the LSP mass to the TeV domain, so that the squark and slepton masses are order 103 TeV and 106 TeV in these two schemes. We study the spectrum, dark matter and collider signals of these two versions of Spread Supersymmetry. The Higgs boson is Standard Model-like and predicted to lie in the range 110-145 GeV; monochromatic photons in cosmic rays arise from dark matter annihilations in the halo; exotic short charged tracks occur at the LHC, at least for the wino LSP; and there are the eventual possibilities of direct detection of dark matter and detailed exploration of the TeV-scale states at a future linear collider. Gauge coupling unification is at least as precise as in minimal supersymmetric theories. If supersymmetry breaking is also mediated at order X, a much less hierarchical spectrum results. The spectrum in this case is similar to that of the Minimal Supersymmetric Standard Model, but with the superpartner masses 1-2 orders of magnitude larger than those expected in natural theories.

Fine-tuning implications of direct dark matter searches in the MSSM

We study theoretical implications of direct dark matter searches in the minimal supersymmetric standard model (MSSM). We assume that no accidental cancellations occur in the spin-independent elastic neutralino-quark scattering cross section, but do not impose any relations among the weak-scale MSSM parameters. We show that direct detection cross section below 10^-44 cm^2 requires the lightest supersymmetric particle (LSP) neutralino to be close to either a pure gaugino or pure Higgsino limit, with smaller cross sections correlated with smaller admixture of the subdominant components. The current XENON100 bound rules out essentially all models in which the lightest neutralino has the Higgsino fraction between 0.2 and 0.8. Furthermore, smaller direct detection cross sections correlate with stronger fine-tuning in the electroweak symmetry breaking sector. In the gaugino LSP scenario, the current XENON100 bound already implies some fine-tuning: for example, at least 10% tuning is required if the LSP mass is above 70 GeV. In both gaugino and Higgsino LSP scenarios, the direct dark matter searches currently being conducted and designed should lead to a discovery if no accidental cancellations or fine-tuning at a level below 1% is present.